A good interface sound for iOS (iPhone, iPads) should accomplish the following things.

Be useful: Your sounds should have a function such as telling the user where they are and what they are doing, or that the app is working and ready to be used.

Emotional resonance: Sounds should have personality and be aligned to the brand. They should elicit emotion – a smile, excitement, anticipation – and communicate the values and benefits of your App and brand.

Distinctiveness: Get rid of the generic zips and zaps. Apps shouldn’t go down the path of the bland one size fits all clicks that polluted the web (flash) experience. It’s boring and people switch off. A way to achieve this distinctiveness is to repurpose your existing assets. However, just as the internet is not TV, iPhones aren’t personal computers, so careful attention needs to be given to how these sounds affect the experience.

So who does it well?

Skype:

Skype keeps it simple. You start up skype and when it’s ready you get the “I’m ready” start-up sound. ‘Yay, Skypes working, I can talk to my friends now, damn that feels good’. Skype connects the App experience with the desktop experience by using the same start-up sound. The familiarity makes you feel comfortable, and leverages the brand equity and reputation built up by the desktop app.

Apple:

Apple have always had a strong emphasis on the ‘total experience’. For example, when they change their OS interface, their website and hardware reflect these changes and vice versa.

Apple have brought their desktop sounds to the iPhone. When you get mail you get the mail ping, when you send mail you get the mail woosh. And it feels good right.

The sounds are non intrusive, personable and useful – meaning we’re more likely to and do keep them turned on, allowing them to reinforce the brand relationship.